A process for preparing high-purity nano-silicon powder from quartz sand by hydrogen plasma reduction.

Abstract

This invention discloses a process for preparing high-purity nano-silicon powder from quartz sand by hydrogen plasma reduction, belonging to the field of nano-silicon powder preparation technology. The process uses quartz sand as raw material and sequentially includes raw material pretreatment, DC plasma arc hydrogen plasma heating reduction and volatilization, radio frequency hydrogen plasma secondary reduction, condensation collection, and post-treatment. This invention utilizes DC plasma arc hydrogen plasma and radio frequency hydrogen plasma in a stepwise synergistic manner on the quartz sand, first reducing silicon dioxide to easily volatile silicon monoxide, then further reducing it to elemental silicon vapor, and finally obtaining nano-silicon powder through staged condensation. This invention uses inexpensive and readily available raw materials, has a simple process flow, low energy consumption, and is environmentally friendly. The prepared nano-silicon powder has a purity ≥99.99%, a particle size of 50-200 nm, and a uniform distribution, making it easy to achieve large-scale industrial production and possessing broad application prospects.

Description

Technical Field

[0001] This invention belongs to the field of nano-silicon powder preparation technology, specifically involving a process for preparing high-purity nano-silicon powder by using quartz sand as raw material and through stepwise synergistic reduction of DC plasma arc hydrogen plasma and radio frequency hydrogen plasma. Background Technology

[0002] Nano-silicon powder has the characteristics of large specific surface area, high surface activity and excellent semiconductor properties, and is widely used in high-end fields such as semiconductor devices, solar cells, lithium-ion battery anode materials, and aerospace materials.

[0003] Currently, the main methods for preparing high-purity nano-silicon powder include chemical vapor deposition (CVD), silane thermal decomposition, mechanical ball milling, and plasma reduction. While CVD and silane thermal decomposition can produce high-purity nano-silicon powder, the raw materials (such as silane and silicon tetrachloride) are expensive, flammable, and explosive, posing safety hazards. Furthermore, the production process easily generates toxic and harmful byproducts, resulting in significant environmental pressure. Mechanical ball milling is simple and low-cost, but the product purity is low, the particle size distribution is uneven, and impurities are easily introduced, making it difficult to meet the high-purity nano-silicon powder requirements of high-end applications. Traditional plasma reduction methods often use a single plasma source with metallic silicon or high-purity silicon dioxide as raw materials, resulting in high raw material costs, incomplete reduction, difficulty in controlling product particle size, and high energy consumption.

[0004] In recent years, there have been attempts to apply plasma technology to the preparation of silicon materials. For example, Chinese patent CN105793193A discloses a method for reducing silicon dioxide using hydrogen plasma. This method involves contacting aggregates containing a silicon oxide layer with hydrogen plasma, reducing the silicon dioxide to gaseous silicon monoxide. Although this patent mentions that the gas used to generate the plasma can be a mixture of hydrogen and argon, with the hydrogen ratio ranging from 0.5% to 50%, its technical solution only involves a single plasma treatment step, and the object of treatment is the silicon oxide layer on the surface of silicon particles, rather than directly preparing nano-silicon powder from quartz sand. The reduction depth and product morphology are fundamentally different from the purpose of this invention. Chinese patent CN101559946B discloses a method for preparing silicon nanoparticles using plasma, using a mixture of a silicon-containing gas source (such as silane) and an inert gas as raw materials, and preparing silicon nanoparticles through plasma conversion. Chinese patent CN102320606B also discloses a method for growing nanocrystalline silicon powder using silane and hydrogen as reactants and argon as the working gas through radio frequency plasma. However, the aforementioned existing technologies all use expensive silicon-containing gases such as high-purity silanes as raw materials, which are costly and pose safety hazards, making it difficult to directly prepare high-purity nano-silicon powder using inexpensive quartz sand as raw material.

[0005] Quartz sand is one of the most abundant minerals in the Earth's crust, with low cost and wide availability. Its main component is silicon dioxide (SiO2), making it an ideal raw material for preparing silicon-based materials. However, due to the presence of small amounts of impurities in quartz sand and the stable chemical properties of silicon dioxide, it is difficult to efficiently reduce it to high-purity silicon. Therefore, current technologies make it difficult to directly prepare high-purity nano-silicon powder from quartz sand.

[0006] Furthermore, existing plasma reduction processes mostly employ a single reduction path, either directly reducing silicon dioxide to elemental silicon, which is difficult and energy-intensive, or producing non-stoichiometric silicon oxides that are difficult to purify further. Simultaneously, the reduction process is prone to problems such as product agglomeration and excessively large particle sizes, affecting product quality. Therefore, developing a high-purity nano-silicon powder preparation process using inexpensive silica sand as raw material, characterized by simplicity, low energy consumption, high product purity, and controllable particle size, has significant industrial application value and market potential. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a process for preparing high-purity nano-silicon powder from quartz sand by hydrogen plasma reduction. Using inexpensive quartz sand as raw material, the process achieves stepwise reduction and purification of silicon dioxide through the synergistic effect of DC plasma arc hydrogen plasma and radio frequency hydrogen plasma, thus solving the problems of high raw material cost, incomplete reduction, low product purity, and uneven particle size in existing processes.

[0008] Technical solution To achieve the above objectives, the present invention adopts the following technical solution: A process for preparing high-purity nano-silicon powder from quartz sand by hydrogen plasma reduction includes the following steps: (1) Raw material pretreatment: The quartz sand raw material is purified to obtain purified quartz sand raw material; (2) Formation and volatilization of silicon monoxide: The purified quartz sand raw material is brought into contact with DC hydrogen plasma in the first reaction zone, so that the silicon dioxide in it is reduced to silicon monoxide, and the conditions are controlled to separate the silicon monoxide from the reaction system in gaseous form. (3) Generation of elemental silicon: The gaseous silicon monoxide generated in step (2) is introduced into the second reaction zone and brought into contact with radio frequency hydrogen plasma, so that it is reduced to generate elemental silicon vapor; (4) Condensation and collection: The elemental silicon vapor generated in step (3) is condensed in stages, the nano silicon powder obtained by condensation is collected, and post-processing is performed to obtain high-purity nano silicon powder finished product.

[0009] Further, in step (1), the raw material pretreatment includes crushing and sieving the quartz sand to a suitable particle size, and then sequentially performing acid washing, water washing, and drying treatment.

[0010] Furthermore, the pickling uses dilute hydrochloric acid or dilute nitric acid with a mass concentration of 5-15%, the pickling temperature is 25-60℃, and the pickling time is 30-90 min; the water washing uses deionized water and is washed until the washing solution is neutral; the drying temperature is 80-120℃, and the drying time is 2-4 h.

[0011] Further, in step (2), the first reaction zone is a DC plasma arc reactor, which generates DC hydrogen plasma by introducing a mixture of high-purity hydrogen and argon into the reactor and starting the DC plasma arc generator.

[0012] Further, in step (2), the purity of the high-purity hydrogen gas is ≥99.999%, the purity of the argon gas is ≥99.999%, and the proportion of hydrogen gas in the total gas is 10~30%. The mixed gas flow rate is 5-20 L / min; the input power of the DC plasma arc generator is 30-80 kW, the arc voltage is 50-120 V, and the arc current is 300-800 A; the reaction temperature is controlled at 1800-2500 ℃, and the reaction vacuum degree is controlled at 1.3×10⁻⁶. -2 -13Pa; the feed rate of the quartz sand raw material is 10-50g / min.

[0013] Furthermore, in step (2), the reduction reaction equation of silicon dioxide with hydrogen plasma is: SiO2 + H + / (H) → SiO↑ + H2O, this reaction proceeds spontaneously under high temperature and low vacuum conditions. DC hydrogen plasma not only provides the high temperature required for the reaction, but its high-energy hydrogen free radicals can also accelerate the reduction reaction. At the same time, the high temperature environment can promote the volatilization or suppression of impurities, ensuring the purity of gaseous silicon monoxide.

[0014] Further, in step (3), the second reaction zone is a radio frequency plasma reactor, which generates radio frequency hydrogen plasma by introducing high-purity hydrogen gas into the reactor and starting the radio frequency plasma generator.

[0015] Further, in step (3), the purity of the high-purity hydrogen is ≥99.999%, the purity of the argon is ≥99.999%, and the mixed gas introduction rate is 3-15L / min; the input power of the radio frequency plasma generator is 20-60kW, and the radio frequency is 13.56MHz; Furthermore, in step (3), the secondary reduction reaction equation of gaseous silicon monoxide with hydrogen plasma is: SiO(g) + H₂ + / (H) → Si + H2O. Radio frequency hydrogen plasma has a higher energy density and a more uniform plasma field, which can fully dissociate and reduce gaseous silicon monoxide, avoiding excessive impurity content in the product due to incomplete reduction. At the same time, it can control the generation rate of elemental silicon vapor, laying the foundation for subsequent condensation to form uniformly sized nano-silicon powder.

[0016] Specifically, the first reaction zone (DC plasma arc reactor) and the second reaction zone (RF plasma reactor) are synergistically matched in terms of process parameters: the reaction temperature of the first reaction zone (1800-2500℃) is higher than that of the second reaction zone (1500-2200℃), while the vacuum degree of the first reaction zone (1.3×10⁻⁶) is lower. -2 -13 Pa) is lower than that of the second reaction zone (1.3 × 10⁻¹³ Pa). -5 -1.3×10 -2 This parameter gradient configuration of "high temperature and low pressure → lower temperature and higher vacuum" can create a pressure gradient for the directional transport of gaseous silicon monoxide from the first reaction zone to the second reaction zone, effectively suppressing the reverse reaction (Si + H2O → SiO + H2) and ensuring that the reaction continues in the direction of generating elemental silicon. Simultaneously, the higher vacuum in the first reaction zone facilitates the rapid volatilization and separation of silicon monoxide, while the even higher vacuum in the second reaction zone promotes the thorough execution of the deep reduction reaction. The synergistic effect of these two factors enables a highly efficient and continuous conversion from quartz sand to high-purity nano-silicon powder.

[0017] Furthermore, in step (4), the condensation collection device adopts a multi-stage condensation structure, with a first-stage condensation temperature of 800-1200℃, a second-stage condensation temperature of 300-600℃, and a third-stage condensation temperature of 20-80℃; the condensation medium is liquid nitrogen or cooling water.

[0018] Further, in step (4), the post-processing includes vacuum drying and inert gas protective packaging of the collected nano-silicon powder; the vacuum drying temperature is 60-100℃, and the vacuum degree is 1.3×10⁻⁶. -3 -1.3×10 -1 The drying time is 1-3 hours; the inert gas is argon or nitrogen with a purity ≥99.999%, and the protective pressure of the inert gas during packaging is 0.1-0.3 MPa.

[0019] Furthermore, the DC plasma arc reactor and the radio frequency plasma reactor are connected by a high-temperature resistant sealed pipe, the inner wall of which is coated with a high-temperature resistant anti-stick coating, and a flow regulating valve is installed on the pipe.

[0020] (1) Stepwise synergistic reduction mechanism: For the first time, DC plasma arc hydrogen plasma and radio frequency hydrogen plasma are synergistically applied to the preparation of nano-silicon powder from quartz sand. The first step utilizes the high temperature and strong reduction characteristics of DC arc to achieve the reduction and gas separation of SiO2→SiO; the second step utilizes the high energy density of radio frequency plasma to achieve the deep reduction of SiO→Si. The stepwise reaction reduces the thermodynamic difficulty of single reduction, improves the reduction efficiency and product purity, and solves the problems of incomplete reduction and high impurity content in traditional single plasma.

[0021] (2) Substitution of inexpensive raw materials: Replacing expensive raw materials such as high-purity silicon or silane in traditional processes with widely available and inexpensive quartz sand significantly reduces production costs. Through pretreatment and step-by-step reduction processes, impurities in quartz sand are effectively removed, ensuring the purity of the final product.

[0022] (3) Gas separation and precise condensation: The high-temperature volatility of silicon monoxide is used to separate the reduction products in gaseous form, avoiding the mixing of solid impurities. Through precise control of radio frequency hydrogen plasma and staged condensation technology, nano-silicon powder with uniform particle size (50-200nm) and good dispersibility is prepared.

[0023] (4) Green and environmentally friendly: Hydrogen is used as the reducing medium, no toxic and harmful byproducts are generated, and hydrogen can be recycled, which meets the requirements of green industrial development.

[0024] Beneficial effects Compared with the prior art, the present invention has the following beneficial effects: (1) The step-by-step synergistic reduction mechanism brings about a synergistic effect of "1+1>2", and with the optimized working gas composition, it achieves a comprehensive balance between reduction efficiency, safety and equipment life. The first step utilizes the high temperature and strong reduction characteristics (1800-2500℃) of DC plasma arc to melt and vaporize SiO2 in quartz sand and reduce it to easily volatile silicon monoxide. At the same time, the high temperature is used to volatilize and separate the metal impurities in the raw materials, achieving preliminary purification. The second step utilizes the high energy density and uniform plasma field of radio frequency hydrogen plasma to deeply reduce gaseous silicon monoxide to elemental silicon vapor. The two reactions are completed within the temperature window that is more thermodynamically feasible, effectively reducing the Gibbs free energy barrier of a single reduction and solving the problem of incomplete reduction by a single plasma. Furthermore, this invention uses a hydrogen-argon mixture with a hydrogen volume ratio of 10%-30% as the working gas. This ratio is an optimal range determined after balancing reduction efficiency, process safety, and equipment lifespan: argon is more easily ionized than hydrogen, which helps to stabilize and maintain plasma ignition; the hydrogen concentration is controlled well below the explosion limit (the explosion limit in air is 4.0%-75.6%), which, combined with the low vacuum environment, significantly improves operational safety; simultaneously, argon, as an inert diluent gas, reduces hydrogen embrittlement of electrode materials at high temperatures, extending equipment lifespan. This synergistic mechanism makes it possible to prepare high-purity nano-silicon powder using inexpensive silica sand as raw material, fundamentally solving the comprehensive technical problems of expensive raw materials, incomplete reduction, poor safety, and short equipment lifespan in traditional processes.

[0025] (2) The raw materials are widely available and inexpensive, and the pretreatment and process work together to ensure high product purity. This invention uses natural quartz sand, which is abundant in the earth's crust, to replace expensive raw materials such as high-purity silicon, silane, or silicon tetrachloride in traditional processes, which greatly reduces production costs. The acid washing pretreatment effectively removes impurities such as metal oxides from the raw materials. Combined with the high-temperature volatilization and gas migration in the two-step plasma reduction process, the impurities are separated from the system before the product condenses, ensuring that the purity of the final product is ≥99.99%, which can meet the requirements of high-end fields such as semiconductors and solar cells.

[0026] (3) The process is simple, continuous and controllable, green and environmentally friendly, and consumes less energy than traditional processes. This invention adopts a continuous process flow of a DC plasma arc reactor and a radio frequency plasma reactor connected in series. The directional transport of gaseous silicon monoxide is achieved through the pressure gradient between the reactors, without the need for additional gas transport power. The process control parameters are clear and the operation is convenient. The entire process uses hydrogen as the reducing medium and water vapor as the reduction byproduct. There are no toxic or harmful gases or waste liquids emitted. The hydrogen can be recycled after separation and purification. At the same time, the thermodynamic design of step-by-step reduction avoids the energy waste caused by single high-temperature treatment. The overall energy consumption is significantly lower than that of traditional plasma reduction processes and silane thermal decomposition methods.

[0027] (4) The product particle size is controllable and the dispersion is good, with broad prospects for industrialization. This invention precisely controls the generation rate of elemental silicon vapor through radio frequency plasma, combined with three-stage staged condensation (800-1200℃→300-600℃→20-80℃), which enables controllable adjustment of the nano-silicon powder particle size in the range of 50-200nm. The product has good dispersion and no obvious agglomeration. The process equipment investment is reasonable, the feasibility of scale-up production is strong, and it is easy to build a production line with a scale of hundreds of tons. The product can be widely used in high-end fields such as lithium-ion battery anode materials and aerospace materials, and has significant market competitiveness and industrial practical value. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the equipment connection for preparing high-purity nano-silicon powder from quartz sand by hydrogen plasma reduction according to the present invention.

[0029] In the diagram: 1- Quartz sand feeding device; 2- DC plasma arc reactor; 3- DC plasma arc generator; 4- High temperature resistant sealed pipe; 5- Radio frequency plasma reactor; 6- Radio frequency plasma generator; 7- Multi-stage condensation and collection device; 8- Vacuum drying device; 9- Inert gas protective packaging device. Detailed Implementation

[0030] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0031] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0032] Example 1

[0033] A process for preparing high-purity nano-silicon powder from quartz sand by hydrogen plasma reduction includes the following steps: (1) Raw material pretreatment: Quartz sand is crushed and sieved to obtain quartz sand particles with a particle size of 50-100μm; the quartz sand particles are placed in dilute hydrochloric acid with a mass concentration of 5% and acid washed at 25℃ for 90min, then washed with deionized water until the washing liquid is neutral, and finally dried at 80℃ for 4h to obtain purified quartz sand raw material. (2) Silica generation and volatilization: The pretreated quartz sand raw material is fed into the DC plasma arc reactor at a feed rate of 10 g / min. A mixture of high-purity hydrogen (99.999%) and high-purity argon (99.999%) is introduced into the reactor. The proportion of the mixed gas is 10% of the total gas, and the introduction rate is 5 L / min. The DC plasma arc generator is started with an input power of 30 kW, an arc voltage of 50 V, and an arc current of 600 A to generate DC hydrogen plasma. The temperature inside the reactor is controlled at 1800 °C and the vacuum is controlled at 13 Pa, so that the quartz sand particles melt and the silica is reduced to generate silica. The silica volatilizes into gaseous silica at high temperature. (3) Generation of elemental silicon: Gaseous silicon monoxide is introduced into the radio frequency plasma reactor through a high-temperature resistant sealed pipe. The flow rate regulating valve on the pipe controls the introduction rate to match the quartz sand feed rate. A mixture of 99.999% high-purity hydrogen and 99.999% high-purity argon is introduced into the reactor, with hydrogen accounting for 10% of the total gas, and the introduction rate is 3L / min. The radio frequency plasma generator is started with an input power of 20kW and a radio frequency of 13.56MHz. The temperature inside the reactor is controlled at 1500℃ and the vacuum degree is controlled at 1.3×10⁻⁶. -2 Pa, gaseous silicon monoxide undergoes a secondary reduction reaction under the action of radio frequency hydrogen plasma to generate elemental silicon vapor; (4) Condensation and Collection: Elemental silicon vapor is introduced into a multi-stage condensation and collection device. The first-stage condensation temperature is 800℃, the second-stage condensation temperature is 300℃, and the third-stage condensation temperature is 20℃. Liquid nitrogen is used as the condensation medium to rapidly condense the elemental silicon vapor into nano-silicon powder. The collected nano-silicon powder is then condensed at 60℃ and a vacuum degree of 1.3×10⁻⁶. -1 Drying at Pa for 3 hours, and then packaging under argon protection (protection pressure 0.1 MPa) with a purity of 99.999% to obtain high-purity nano-silicon powder.

[0034] Testing showed that the high-purity nano-silicon powder prepared in this embodiment had a purity of 99.99%, a particle size of 50-150 nm, good dispersibility, and no obvious agglomeration.

[0035] Example 2

[0036] A process for preparing high-purity nano-silicon powder from quartz sand by hydrogen plasma reduction includes the following steps: (1) Raw material pretreatment: Quartz sand is crushed and sieved to obtain quartz sand particles with a particle size of 100-150μm; the quartz sand particles are placed in dilute nitric acid with a mass concentration of 10% and acid washed at 40℃ for 60min, then washed with deionized water until the washing liquid is neutral, and finally dried at 100℃ for 3h to obtain purified quartz sand raw material; (2) Silica generation and volatilization: The pretreated quartz sand raw material is fed into the DC plasma arc reactor at a feed rate of 30 g / min. A mixture of high-purity hydrogen (99.999%) and high-purity argon (99.999%) is introduced into the reactor. The proportion of the mixed gas is 20% of the total gas, and the introduction rate is 12 L / min. The DC plasma arc generator is started with an input power of 50 kW, an arc voltage of 80 V, and an arc current of 625 A to generate DC hydrogen plasma. The temperature inside the reactor is controlled at 2200 °C and the vacuum degree is controlled at 1.3 Pa, so that the quartz sand particles melt and the silica is reduced to generate silica. The silica volatilizes into gaseous silica at high temperature. (3) Generation of elemental silicon: Gaseous silicon monoxide is introduced into the radio frequency plasma reactor through a high-temperature resistant sealed pipe. The flow rate regulating valve on the pipe controls the introduction rate to match the quartz sand feed rate. A mixture of 99.999% high-purity hydrogen and 99.999% high-purity argon is introduced into the reactor, with hydrogen accounting for 20% of the total gas, and the introduction rate is 9 L / min. The radio frequency plasma generator is started with an input power of 40 kW and a radio frequency of 27.12 MHz. The temperature inside the reactor is controlled at 1800 ℃ and the vacuum degree is controlled at 1.3 × 10⁻⁶. -4 Pa, gaseous silicon monoxide undergoes a secondary reduction reaction under the action of radio frequency hydrogen plasma to generate elemental silicon vapor; (4) Condensation and Collection: Elemental silicon vapor is introduced into a multi-stage condensation and collection device. The first-stage condensation temperature is 1000℃, the second-stage condensation temperature is 450℃, and the third-stage condensation temperature is 50℃. Cooling water is used as the condensation medium to rapidly condense the elemental silicon vapor into nano-silicon powder. The collected nano-silicon powder is then condensed at 80℃ and a vacuum degree of 1.3×10⁻⁶. -2 Drying at 0.2 MPa for 2 hours, and then packaging under nitrogen protection (0.2 MPa) with a purity of 99.999%, yields high-purity nano-silicon powder.

[0037] Testing showed that the high-purity nano-silicon powder prepared in this embodiment had a purity of 99.995%, a particle size of 80-180 nm, good dispersibility, and no obvious agglomeration.

[0038] Comparative Example 1 (Single DC hydrogen plasma process) A single DC plasma arc hydrogen plasma reduction process was employed, using quartz sand pretreated in the same manner as in Example 1 as the raw material. Nano-silicon powder was directly prepared by reduction under the same conditions (temperature 1800℃, vacuum 13Pa, hydrogen content in the mixed gas 10%, mixed gas flow rate 5L / min, power 30kW), without a secondary reduction step via radio frequency hydrogen plasma. The results showed that the silicon content in the product was only 85-90%, containing a large amount of unreacted silica and the intermediate product silica, making it impossible to obtain high-purity nano-silicon powder.

[0039] Comparative Example 2 (Single RF hydrogen plasma process) A single radio frequency hydrogen plasma reduction process was employed, using quartz sand pretreated in the same manner as in Example 1 as the raw material. The quartz sand powder was directly fed into the radio frequency plasma reactor, and the process was carried out at a temperature of 1800°C and a vacuum of 1.3 × 10⁻⁶. -2 The reduction reaction was carried out under the conditions of Pa, mixed gas flow rate of 8 L / min, power of 30 kW, and frequency of 13.56 MHz. The results showed that, due to the much lower heating efficiency of radio frequency plasma on solid powder compared to a DC arc, the quartz sand particles were difficult to completely melt. The reaction was mainly a solid-phase interface reaction, with an extremely low reaction rate. Most of the quartz sand did not participate in the reaction, and the silicon content in the product was less than 10%, making effective reduction impossible. This comparative example illustrates that a single radio frequency hydrogen plasma process cannot directly process solid quartz sand raw materials; it must rely on the high-temperature melting and vaporization effect of the first step, DC arc plasma.

[0040] Comparative Examples 1 and 2 show that the two-step synergistic process of "DC arc hydrogen plasma (high temperature vaporization) + radio frequency hydrogen plasma (deep reduction)" of the present invention produces an unexpected technical effect of "1+1>2", which not only solves the problem of incomplete reduction by DC arc alone, but also overcomes the defect that radio frequency plasma alone cannot effectively process solid raw materials.

[0041] Industrial applicability The process of this invention uses inexpensive quartz sand as raw material and prepares high-purity nano-silicon powder through stepwise plasma reduction technology. The process is stable, highly repeatable, and easy to scale up for production. Using this process, a production line with an annual output of hundreds of tons of high-purity nano-silicon powder can be built. The product can be widely used in high-end fields such as semiconductors, solar cells, lithium-ion batteries, and aerospace, and has significant industrial practical value and market competitiveness.

[0042] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for preparing high-purity nano-silicon powder from quartz sand by hydrogen plasma reduction, characterized in that, Includes the following steps: (1) Raw material pretreatment: The quartz sand raw material is purified to obtain purified quartz sand raw material; (2) Formation and volatilization of silicon monoxide: The purified quartz sand raw material is brought into contact with DC hydrogen plasma in the first reaction zone, so that the silicon dioxide in it is reduced to silicon monoxide, and the conditions are controlled to separate the silicon monoxide from the reaction system in gaseous form. (3) Generation of elemental silicon: The gaseous silicon monoxide generated in step (2) is introduced into the second reaction zone and brought into contact with radio frequency hydrogen plasma, so that it is reduced to generate elemental silicon vapor; (4) Condensation and collection: The elemental silicon vapor generated in step (3) is condensed in stages, the condensed nano-silicon powder is collected, and post-processed to obtain high-purity nano-silicon powder product.

2. The process according to claim 1, characterized in that, In step (1), the raw material pretreatment includes crushing and sieving the quartz sand to a particle size of 50-200μm, and then sequentially performing acid washing, water washing and drying treatment.

3. The process according to claim 2, characterized in that, The pickling process uses dilute hydrochloric acid or dilute nitric acid with a mass concentration of 5-15%, the pickling temperature is 25-60℃, and the pickling time is 30-90 minutes; the water washing process uses deionized water and continues until the washing solution is neutral; the drying temperature is 80-120℃, and the drying time is 2-4 hours.

4. The process according to claim 1, characterized in that, In step (2), the first reaction zone is a DC plasma arc reactor. The DC hydrogen plasma is generated by introducing a mixture of high-purity hydrogen and argon into the reactor and starting the DC plasma arc generator.

5. The process according to claim 4, characterized in that, In step (2), the purity of the high-purity hydrogen gas is ≥99.999%, and the purity of the argon gas is ≥99.999%, with hydrogen accounting for 10-30% of the total gas. The mixed gas flow rate is 5-20 L / min; the input power of the DC plasma arc generator is 30-80 kW, the arc voltage is 50-120 V, and the arc current is 300-800 A; the reaction temperature is controlled at 1800-2500 °C, and the reaction vacuum degree is controlled at 1.3 × 10⁻⁶. -2 -13Pa; the feed rate of the quartz sand raw material is 10-50g / min.

6. The process according to claim 1, characterized in that, In step (3), the second reaction zone is a radio frequency plasma reactor. The radio frequency hydrogen plasma is generated by introducing high-purity hydrogen-argon gas into the reactor and starting the radio frequency plasma generator, wherein the proportion of hydrogen gas in the total gas is 10-30%.

7. The process according to claim 6, characterized in that, In step (3), the purity of the high-purity hydrogen is ≥99.999%, the purity of the argon is ≥99.999%, and the mixed gas flow rate is 3-15L / min; the input power of the radio frequency plasma generator is 20-60kW, and the radio frequency is 13.56MHz.

8. The process according to claim 1, characterized in that, In step (4), the staged condensation adopts a multi-stage condensation structure, with the first-stage condensation temperature being 800-1200℃, the second-stage condensation temperature being 300-600℃, and the third-stage condensation temperature being 20-80℃; the condensation medium is liquid nitrogen or cooling water.

9. The process according to claim 1, characterized in that, In step (4), the post-processing includes vacuum drying and inert gas protective packaging of the collected nano-silicon powder; the vacuum drying temperature is 60-100℃, and the vacuum degree is 1.3×10⁻⁶. -3 -1.3×10 -1 The drying time is 1-3 hours; the inert gas is argon or nitrogen with a purity ≥99.999%, and the protective pressure of the inert gas during packaging is 0.1-0.3 MPa.

10. The process according to any one of claims 1-9, characterized in that, The DC plasma arc reactor and the radio frequency plasma reactor are connected by a high-temperature resistant sealed pipe. The inner wall of the pipe is coated with a high-temperature resistant anti-stick coating, and a flow regulating valve is installed on the pipe.

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